The group weblog for students in Physiology for Bioengineers (VTPP 434 and 435) at Texas A&M University

Thursday, April 17, 2008

Used Meth? Tired of It? Just Reboot.

Research has shown that methamphetamine stimulates release of dopamine by neurons in the midbrain into the synapses of nerve cells in the striatum, the region of the forebrain associated with control of movement, but most notably the development of habitual behaviors. This excess dopamine - a neurotransmitter connected to motivation and attention - then inhibits information flow from the cortex to the affected area by blocking nerve cells in the cortex from releasing the neurotransmitter glutamate, which is primarily responsible for excitation. Thus a possible explanation for the addictive nature of methamphetamines arises: the increased levels of dopamine combined with the inhibition of messages from the cortex allows the addict to focus his attention on one particular object or stimulus, namely the pleasurable stimulus of the drug.

Most recently, researchers using mice discovered that although simply discontinuing use of the drug does not return the brain to its pre-addicted state, the brain does return to its pre-addicted after a reintroduction of the drug, in effect "resetting" the system. These results were obtained from mice given methamphetamines for 10 days, which translates into about 2 years of human use. After the mice had been in withdrawal, a single final dose produced the noted the results. These results are believed to have some correlation with other neurons found in the striatum that release acetylcholine: methamphetamines cause increased release of dopamine, which depresses acetylcholine levels, which in turn causes a depression of glutamate levels, resulting in the depression of information flow in the brain. Re-administration of methamphetamines after a period of withdrawal, however, somehow has the reverse effect on the acetylcholine produces neurons. Consequently, research is underway to locate and identify this neuronal "reset button".

This is yet another illustration of the remarkable complexity of the brain.